1. Field of Invention
The present invention relates to a hub structure, and more particularly to a silent hub structure.
2. Description of Related Art
Currently, the conventional hub for bicycles relies on the ratchet mechanism to achieve the goal of having the hub to act in a continuous linear or rotary motion in only one direction. However, such hub structure generates backlash noise during a backward motion. In order to eliminate the noise, industrial manufacturers have developed silent hubs. Please refer to the illustrations in FIG. 10 and FIG. 11. The hub 50 has a clutch device disposed between the clutch housing 51 and the cassette base 52, wherein the clutch device is composed of receiving groove 53 located inside the cassette base 52, the roller pin 54 located inside the receiving groove 53, and the elastic member 55 (as shown in FIG. 11). Furthermore, the receiving groove 53 has a contracting inclined surface and a clamping portion 531 formed at the end of the inclined surface. In use of the design, as the bicycle is pedaled, the cassette base 52 is in a forward-rotating mode; through the push against and frictional movement by the elastic member 55 inside the receiving groove 53, the roller pin 54 moves toward the direction of clamping portion 531 of the receiving groove 53 and reaches a clamping stop, forcing the cassette base 52 and the clutch housing 51 to form a complete engagement through the roller pin 54. By means of such movement, the momentum generated by pedaling is absorbed by the cassette base 52 and transferred to the clutch housing 51, in order to drive the hub 50 to rotate and the bicycle to move forward.
On the other hand, when the user slows down and steps the pedals backward, the cassette base 52 and the clutch housing 51 in rotation are moving in an opposite rotation direction and further roll out the roller pin 54 from the clamping portion 531 of the receiving groove 53 through the cassette base 52, forcing the cassette base 52 and the clutch housing 51 to be released from the engagement mode and to become rotating in idle. Since the clutch housing 51 is still in the forward-rotating move, the bicycle is sliding in a free spinning mode.
According to the aforementioned structure of the prior art, it is apparent that there are few deficiencies due to the following facts: (1) The structure of the prior art has a roller pin 54 disposed in each of the plurality of receiving groove 53 separately to provide the effect of engagement and disengagement between the clutch housing 51 and the cassette base 52. Every receiving groove 53 is installed with a elastic member 55 therein to provide the elastic effect of resetting the roller pin 54. However, the elastic member 55 is compressed to a very small scale within the much limited space provided in the receiving groove 53. Therefore, not only the volume of the elastic member 55 reduces, but also its elasticity deteriorates due to a long period of compression and will no longer be sufficient to provide the elastic resetting effect to the roller pin.
(2) In addition, the elastic member 55 in the receiving groove 53 is in contact with both the clutch housing 51 and the cassette base 52. When the cassette base 52 is released from the engagement mode with the clutch housing 51, the clutching house 51 still is rotating in idle with respect to the cassette base 52, causing the elastic member 55 to be under friction from the rotating cassette base 52. As a result, the rotation of the cassette base 52 is interfered by the resistance and heat is generated due to the friction, causing the elastic member 55 to become possible thermal embrittlement and to change its physical characteristics to less elastic, and to have more damage and a shorter service life.
In view of this, the author of the present invention has many years of experience in design, development, and production of relevant products and set to find the solutions for the aforementioned deficiencies. After a careful design and evaluation, the present invention with practicality is developed.